Phosphazenes have both the good flame retardant property of phosphorus flame retardant and flame retardant synergism of nitrogen compound. Without the need to add any other assisting flame retardants, they have advantages like good flame retardant efficiency, good thermal stability, no toxicity, less smoke and self-extinguishment and are therefore generally recognized as one of the future development directions of fire retardant. Various kinds of phosphazene flame retardants are synthesized and used in flame retardant research of various materials. At the same time, phosphazenes can also be used in preparation of high temperature resistant, low temperature resistant and oxidation resisting special rubber and elastic materials used in military and aerospace industries. Chloro-cyclotriphosphazene has good flame retardant efficiency. However, it has easy hydrolysis and chlorine is highly corrosive to battery system. Recently, it is found in research that replacing chlorine with fluorine can get a functional phosphazene derivative with hydrolysis resistance, lower viscosity and better compatibility. Fluoro-phosphazenes can also be used as an efficient flame retardant for lithium ion battery. Currently, phosphazenes are usually fluoridized in organic small molecule solvent and then make distillation and fractionation to the fluoride generated. As the organic small molecule is volatile and forms azeotrope with fluoro-cyclotriphosphazene, which makes purification difficult. It wastes solvents and increases cost.